1. Field of the Invention
The present invention relates to an electroconductive resin composition, sheet, molded product and container. More particularly, it relates to an electroconductive resin composition having an olefin type resin incorporated to an electroconductive rein composition comprising carbon black and at least one thermoplastic resin selected from the group consisting of a polyphenylene ether type resin, a polystyrene type resin and an ABS type resin, so that staining of e.g. IC caused by falling off of e.g. carbon black by abrasion at the time of contact with e.g. IC is substantially reduced, and an electroconductive sheet, molded product and container made thereof.
2. Discussion of Background
As packaging containers for IC or electronic parts using IC, injection-molded trays, vacuum-formed trays, magazines, embossed carrier tapes, etc. have been used. To prevent breakage of IC, etc. due to static electricity, these packaging containers have been treated by, e.g., (1) a method of coating an antistatic agent on the surface of the packaging containers, (2) a method of coating an electroconductive paint, (3) a method of dispersing an antistatic agent, or (4) a method of dispersing an electroconductive filler.
Method (1) provides a sufficient antistatic effect immediately after the coating. However, during the use for an extended period of time, the antistatic agent tends to flow out due to moisture or tends to be lost by abrasion, whereby a constant performance can not be obtained. Further, the surface resistivity is at a level of from 10.sup.9 to 10.sup.12 .OMEGA., which is not satisfactory for packaging IC, where a high level of an antistatic effect is required.
Method (2) has a drawback that during the preparation, coating tends to be non-uniform, and the coated paint is likely to fall off by abrasion, whereby the antistatic effect will be lost, thus leading to breakage of IC, and the lead of IC tends to be stained.
Method (3) has a demerit in that it is necessary to incorporate a large amount of an antistatic agent, whereby the physical properties of the resin will deteriorate, and the surface resistivity will be substantially affected by humidity, whereby a constant performance can hardly be obtained.
In method (4), the electroconductive filler may, for example, be fine metal powder, carbon fiber or carbon black. With fine metal powder and carbon fiber among them, adequate electroconductivity can be obtained with a small amount of incorporation, but the moldability will thereby substantially deteriorate, and it is difficult to uniformly disperse them. Further, a skin layer composed solely of the resin component is likely to form on the surface of a molded product, and it is difficult to obtain a constant surface resistivity.
Whereas, carbon black can be uniformly dispersed by properly selecting the kneading conditions, etc., whereby a constant surface resistivity can easily be obtained. For this reason, carbon black is most commonly employed. However, carbon black is required to be incorporated in a large amount, whereby the fluidity or the moldability tends to deteriorate.
As resins for dispersing carbon black therein, a polyvinyl chloride type resin, a polypropylene type resin, a polyethylene terephthalate type resin, a polystyrene type resin and an ABS type resin have been used as resins of general use, and a polyphenylene ether type resin and a polycarbonate resin have been used as heat resistant resins for use at a temperature of 100.degree. C. or higher. Among these resins, a polystyrene type resin and an ABS type resin as resins of generally use, and a polyphenylene ether type resin as a heat resistant resin, are superior to other resins in that no substantial deterioration in the fluidity or moldability is observed even when carbon black is incorporated therein in a large amount, and they are also excellent from the viewpoint of costs. However, compositions obtained by adding a large amount of carbon black to these resins, have had a drawback that carbon black is likely to fall off from the surface of their molded products by abrasion.